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Interaction of electrons with matter Interaction of photons with matter

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## Interaction of electrons with matter Interaction of photons with matter

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**Part B. Radiation sources**• Interaction of electrons with matter • Interaction of photons with matter • Interaction of neutrons with matter • Interaction of protons with matter**1. Interaction of electrons with matter**The physical processes: 1. Ionization losses inelastic collisions with orbital electrons 2. Bremsstrahlung losses inelastic collisions with atomic nuclei 3. Rutherford scattering elastic collisions with atomic nuclei Positrons at nearly rest energy: annihilation emission of two 511 keV photons**1. Interaction of electrons with matter**Graphite – Z = 6 Electrons – stopping power Copper – Z = 29 Lead – Z = 82**1. Interaction of electrons with matter**Continuous Slowing Down Approximation range: Radiation yield: Fraction of the initial kinetic energy that is converted to Bremsstrahlung energy as the electron slows down to rest.**1. Interaction of electrons with matter**Differential Bremsstrahlung cross section: mbarn mbarn lead – Z = 82 k/T k: photon energy T: electron kinetic energy carbon – Z = 6 k/T**1. Interaction of electrons with matter**Multiple scattering mean scattering angle mass scattering power Ssc Es = 21.2 MeV X0: radiation length β: v/c p: momentum**2. Interaction of photons with matter**The physical processes: 1. Photo-electric effect removal of an orbital electron of the inner shells (K,L,M) 2.Compton scattering inelastic scattering on loosely bound electrons 3.Pair production production of e-/e+ pair essentially with nuclei 4.Rayleigh (coherent) scattering elastic scattering not important for radiation physics**2. Interaction of photons with matter**Photon cross sections Graphite - Z = 6**2. Interaction of photons with matter**Photon cross sections Lead - Z = 82**2. Interaction of photons with matter**Photo-electric effect: photo-electron ΔE = E0 – E1 = Ka ΔE = E – E0 ΔE = E0 – E2 = Kb E2 E0 E1 E0 E K L M N K L M N incoming X-ray The K lines ΔE = E1 – E2 = La Auger-electron E1 E1 ΔE = E1 – E2 – E3 E2 E2 ΔE = E1 – E3 = Lb K L M N K L M N E3 E3 The L lines Auger electron**2. Interaction of photons with matter**Compton scattering: scattered photon energy Ec θ Compton electron energy = E0 - Ec primary photon energy E0 dσ/dW (re2 x cm2 / electron) Ec (MeV)**2. Interaction of photons with matter**Pair production: σnucleus Z2 threshold: 1.022 MeV σelectron Z threshold: 2.044 MeV**2. Interaction of photons with matter**Interaction of photons with matter Macroscopic description - Attenuation factors The mass attenuation coefficient μ/ρ: units: cm2.g-1 The linear attenuation coefficient μ: units: cm-1 The conversion factor from σ (barns.atom-1) to μ/r (cm2.g-1): N d (cm) d (g.cm-2)**Particles involved:**Electrons / Positrons Photons Neutrons 2. Interaction of photons with matter**2. Interaction of photons with matter**Electromagnetic cascade cm one 500 MeV electron interacting with lead target**2. Interaction of photons with matter**Electromagnetic cascade cm one 6 GeV electron interacting with lead target**2. Interaction of photons with matter**photonuclear reactions Photonuclear reactions: Neutron production Photo-pion γ(d,p)n Quasi-deuteron Giant resonance m e-60/E sγ(d,p)n 55Mn(γ, n)54Mn**2. Interaction of photons with matter**Photonuclear reactions: Neutron production Giant resonance Quasi-deuteron Photo-pion Example: neutron spectrum produced by 600 MeV electrons on Cu target**3. Interaction of neutrons with matter**The physical processes: • 1. Elastic scattering • compound elastic scattering • potential scattering • 2. Inelastic scattering (n,n’) • 3. Other inelastic reactions: (n,p), (n,a), … • 4. Absorption reactions • radioactive capture • charged particle reactions • 5. Direct reactions: spallation**3. Interaction of neutrons with matter**Compound nucleus formation target nucleus ZA neutron energy = EC**3. Interaction of neutrons with matter**Neutron cross sections Example 1: iron**3. Interaction of neutrons with matter**Neutron cross sections Example 2: cadmium**3. Interaction of neutrons with matter**Neutron cross sections Example 3: hydrogen**3. Interaction of neutrons with matter**Neutron cross sections Example 4: boron**3. Interaction of neutrons with matter**Neutron cross sections inelastic cross section (barn) Example: iron neutron energy (GeV)**3. Interaction of neutrons with matter**scattered neutron energy = E1 Elastic scattering target nucleus initial neutron energy = E0 recoiling nucleus Minimum energy of scattered neutron: Average energy loss per collision:**4. Interaction of protons with matter**The physical processes: • ionization • inelastic proton-nucleus scattering • spallation**4. Interaction of protons with matter**Proton ionization loss – Stopping power stopping power (MeV.g-1.cm2) minimum ionizing particle proton energy (MeV)**4. Interaction of protons with matter**Comparison CSDA range of protons and electrons in iron**4. Interaction of protons with matter**Inelastic proton – nucleus scattering: Spallation reaction n n p π Δ π incident proton (GeV range) n p intra-nuclear cascade α d n evaporation γ**4. Interaction of protons with matter**Inelastic proton – nucleus scattering Spallation reaction Inelastic cross section E > 1 GeV**4. Interaction of protons with matter**Inelastic proton – nucleus scattering Comparison ionization energy loss and inelastic scattering E > 1 GeV: 100 % probability for spallation reaction**4. Interaction of protons with matter**n inter-nuclear cascades Spallation n p π Δ π incident proton (GeV range) n p intra-nuclear cascade Neutron transport below 20 MeV evaporation α d α spallation product α, β, γ decay n fast induced fission γ p γ n n n fission n n n fission products fission products (n,n’), (n,xn), (n, γ) ,… reactions γ γ**4. Interaction of protons with matter**Spallation